Oxygen Reduction on Gas‐Diffusion Electrodes for Phosphoric Acid Fuel Cells by a Potential Decay Method

Li, Qingfeng; Xiao, Gang; Hjuler, Hans Aage; Berg, Rolf W.; Bjerrum, Niels

doi:10.1149/1.2049970

Cited by 19 publications

(7 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Similar effects of reduced site blocking were described in the literature for perfluoroalkylated sulfonic acid additives 9,34,35 and other perfluorinated compounds. 10,36 With the trifluoromethyl group, the number of proton donating groups within the molecule decreases while the acidity of the corresponding acid simultaneously increases. 37 No significant impact of the alkyl chain length on the electrocatalytic activity for the ORR on polycrystalline Pt was observed in this study (see Section 3.3) and elsewhere, 38 indicating that the lower number of hydroxyl species coordinated to phosphorus is the main reason for the weaker adsorption and enhanced ORR activity.…”

Section: Methodsmentioning

confidence: 99%

“…6 To improve the ORR activity and selectivity, weaker adsorbing anions such as perchlorate, fluoride, or hydroxyl are more favorable than strongly adsorbing anions. 6 In the quest for alternative electrolytes that have a lower tendency to specifically adsorb on the electro-catalyst surface, trifluoromethyl-sulfonic acid (TFMSA) 8,9 and a variety of fluorinated compounds 10 were studied systematically, so that their impact on the ORR kinetics could be explored. With these fluorinated model compounds, enhanced ORR reaction rates were observed due to reduced adsorption enthalpies and higher oxygen solubility compared with phosphoric acid.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Perfluoroalkyl-Phosphonic Acid Adsorption on Polycrystalline Platinum and Its Influence on the Oxygen Reduction Reaction

et al. 2015

View full text Add to dashboard Cite

Motivated by the need for a better understanding of the oxygen reduction reaction (ORR) in high temperature proton exchange membrane fuel cells (HTPEM-FC), we have investigated the impact of anion adsorption on the ORR activity and selectivity for small concentrations of perfluoroalkylated phosphorus based model compounds.A polycrystalline Pt surface was used to evaluate the adsorption behaviour of trifluoromethyl-phosphonic acid (TFMPA) and pentafluoroethyl-phosphonic acid (PFEPA) by means of cyclic voltammetry (CV), a rotating disc electrode (RDE), and a spectro-electrochemical flow cell. In-situ Fourier transform infrared spectroscopy in the attenuated total reflection (ATR-FTIRS) configuration was performed to study the impact of the adsorbed species on the ORR activity and selectivity employing simultaneous detection of hydrogen peroxide formation during the ORR.Electrochemical impedance spectroscopy (EIS) was applied to determine the charge transfer resistance R CT under ORR conditions. The presence of TFMPA, PFEPA or H 3 PO 4 had significant effects on the cyclic voltammograms in the H upd and oxide formation potential region. The ORR activity, measured under well-defined mass transport conditions, revealed a doubling of the kinetic current densities for TFMPA and PFEPA compared with H 3 PO 4 , suggesting a weaker adsorption tendency for these model compounds. The ORR selectivity was found to be dependent on the nature of the adsorbed species. These observations are consistent with ATR-FTIRS and EIS results, where the reduced interaction of perfluoroalkylated compounds with the Pt surface was observed compared to H 3 PO 4 . . IntroductionSustainable energy sources are of growing interest due to environmental regulations and increasing energy consumption worldwide. To satisfy the need for clean energy, fuel cells, which convert chemical energy directly into electrical energy, are promising for both stationary and mobile applications, where high power densities are required.Compared with conventional proton exchange membrane fuel cells (PEM-FC) operated below 100 °C 1 , high-temperature operation (150 -180°C) holds certain advantages, including an increased overall efficiency, a reduced sensitivity to catalyst poisoning, and simplified water management 2 .Under such operating conditions, concentrated phosphoric acid is usually used as the common electrolyte because of its favorable physical and chemical properties at high temperatures. However, the slow ORR in phosphoric acid electrolyte causes a relatively high overpotential on the cathode side 3 , which limits the performance and practical applications of high temperature proton exchange membrane fuel cells (HTPEM-FC). The anions adsorbed at the electrode surface are known to strongly affect the ORR kinetics by occupying catalyst surface sites and hindering the dissociative adsorption of molecular oxygen 4-7 . Hence, they act as site-blocking spectator species. The anions also affect the ORR selectivity by changing the ORR pathway and promote the productio...

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Perfluoroalkyl-Phosphonic Acid Adsorption on Polycrystalline Platinum and Its Influence on the Oxygen Reduction Reaction

et al. 2015

View full text Add to dashboard Cite

show abstract

“…It was noted that the C6 salt led to a stable performance increase for more than three months. The same research group continued to investigate the addition of the C6 salt over the next few years [124][125][126].…”

Section: Additivesmentioning

confidence: 99%

Catalyst, Membrane, Free Electrolyte Challenges, and Pathways to Resolutions in High Temperature Polymer Electrolyte Membrane Fuel Cells

2017

View full text Add to dashboard Cite

High temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are being studied due to a number of benefits offered versus their low temperature counterparts, including co-generation of heat and power, high tolerance to fuel impurities, and simpler system design. Approximately 90% of the literature on HT-PEM is related to the electrolyte and, for the most part, these electrolytes all use free phosphoric acid, or similar free acid, as the ion conductor. A major issue with using phosphoric acid based electrolytes is the free acid in the electrodes. The presence of the acid on the catalyst sites leads to poor oxygen activity, low solubility/diffusion, and can block electrochemical sites through phosphate adsorption. This review will focus on these issues and the steps that have been taken to alleviate these obstacles. The intention is this review may then serve as a tool for finding a solution path in the community.

show abstract

“…In this work, the double-layer capacitance per unit wetted area in the catalyst layer designated as c dl was taken from the experimentally measured data of a PAFC electrode with 0.5 mg Pt/cm 2 and 40% PTFE in its catalyst layer, which was prepared from 10% platinum supported on Vulcan XC-72 carbon. 13 If c dl is known, the specific double-layer capacitance in the catalyst layer C dl is calculated by…”

Section: Ac Impedance Modelmentioning

confidence: 99%

Modeling and Simulation of Steady-State Polarization and Impedance Response of Phosphoric Acid Fuel-Cell Cathodes with Catalyst-Layer Microstructure Consideration

Yang

2000

J. Electrochem. Soc.

View full text Add to dashboard Cite

A porous gas-diffusion electrode model considering the microstructure characteristics of the catalyst layer has been developed. The model is utilized to simulate the dc and ac responses of a reported high-performance phosphoric acid fuel cell (PAFC) cathodes developed by Watanabe et al. [J. Electroanal. Chem., 195, 81 (1985)]. For these electrodes with 30 and 40% poly(tetrafluoroethylene) in the catalyst layers, the dc performance predictions are in good agreement with the experimental behavior. The dc modeling and simulation results suggest that the necessary microstructure characteristics in the catalyst layer of high performance gas diffusion electrodes for PAFCs include (i) a sufficient amount of electrolyte to fill in the primary pores and to wet the secondary pore surface on the condition that no electrolyte flooding takes place in the secondary pores and (ii) a large secondary-pore surface area available in the catalyst layer. The qualitative characteristics of the catalyst layers of these electrodes are analyzed and interpreted by means of the simulated electrode ac responses at several electrode operating conditions.

show abstract

Oxygen Reduction on Gas‐Diffusion Electrodes for Phosphoric Acid Fuel Cells by a Potential Decay Method

Cited by 19 publications

References 12 publications

Perfluoroalkyl-Phosphonic Acid Adsorption on Polycrystalline Platinum and Its Influence on the Oxygen Reduction Reaction

Perfluoroalkyl-Phosphonic Acid Adsorption on Polycrystalline Platinum and Its Influence on the Oxygen Reduction Reaction

Catalyst, Membrane, Free Electrolyte Challenges, and Pathways to Resolutions in High Temperature Polymer Electrolyte Membrane Fuel Cells

Modeling and Simulation of Steady-State Polarization and Impedance Response of Phosphoric Acid Fuel-Cell Cathodes with Catalyst-Layer Microstructure Consideration

Contact Info

Product

Resources

About